2,3,3',4,4',5'-Hexachlorobiphenyl is one of 209 polychlorinated biphenyls (PCBs). PCBs are a group of synthetic organic compounds with 1-10 chlorine atoms attached to biphenyl. They were manufactured as commercial mixtures but banned in the 1970's because they were found to bioaccumulate and cause harmful health effects. However, PCBs do not break down readily and are still found in the environment. (6)
belongs to the class of organic compounds known as polychlorinated biphenyls. These are organic compounds containing at least two chlorine atoms attached to either benzene ring of the biphenyl moiety.
The mechanism of action varies with the specific PCB. Dioxin-like PCBs bind to the aryl hydrocarbon receptor, which disrupts cell function by altering the transcription of genes, mainly be inducing the expression of hepatic Phase I and Phase II enzymes, especially of the cytochrome P450 family. Most of the toxic effects of PCBs are believed to be results of Ah receptor binding. Other PBCs are believed to interfere with calcium channels and/or change brain dopamine levels. PCBs can also cause endocrine disurption by altering the production of thyroid hormones and binding to estrogen receptors, which can stimulate the growth of certain cancer cells and produce other estrogenic effects, such as reproductive dysfunction. They will bioaccumulate by binding to receptor proteins such as uteroglobin. (1, 2, 4, 5)
Metabolism
PCBs are absorbed via inhalation, oral, and dermal routes of exposure. They are trasported in the blood, often bound to albumin. Due to their lipophilic nature they tend to accumulate in lipid-rich tissues, such as the liver, adipose, and skin. Metabolism of PCBs is very slow and varies based on the degree and position of chlorination. PCBs are metabolized by the microsomal monooxygenase system catalyzed by cytochrome P-450 enzymes to polar metabolites that can undergo conjugation with glutathione and glucuronic acid. The major metabolites are hydroxylated products which are excreted in the bile and faeces. The slow metabolism of PCBs means they tend to accumulate in body tissues. (6, 9)
PCBs were used as coolants and lubricants in transformers, capacitors, and other electrical devices (such as fluorescent lights and refridgerators) produced before 1977. PCBs may contaminate the air and water near hazardous waste sites. In addition, PCBs bioaccumulate in the environment and may be found in fish, meat, and dairy products. (6)
The most common health effects of PCBs are skin conditions such as chloracne and rashes. Chronic PCB exposure has also been shown to cause liver, stomach and kidney, damage, jaundice, edema, anemia, changes in the immune system, behavioral alterations, and impaired reproduction. (6)
Symptoms
Chronic PCB exposure results in symptoms such as abdominal pain, nausea, vomiting, diarrhea, headache, dizziness, depression, nervousness, dermal and ocular lesions, fatigue, irregular menstrual cycles and a lowered immune response. (1)
Treatment
There are no specific treatments for PCB poisoning, since it is not usually recognized until after substantial chronic exposure. Only preventing further exposure and treating the observed symptoms can be done. Acute inhalation can be treated by administering oxygen. (6)
